Date: Wed, 10 Dec 2003 20:42:08 -0500 Reply-To: Maryland Birds & Birding Sender: Maryland Birds & Birding From: Gail Mackiernan Subject: Re: Migration, genetics and feeders In-Reply-To: <009301c3bf6b$0231f460$b9a1c7cf@mdatlasxz1p6g> Mime-version: 1.0 Content-type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit An addendum to the Blackcap story os that on 12/10/2003 5:14 PM, Walter Ellison at rossgull@CROSSLINK.NET wrote: > Hi Everybody, > > There are good fairly non-technical discussions of the genetics and > learned components of migration in a couple of recent books - > "Gatherings of Angels: Migrating birds and their ecology", edited by > Ken Able and published by Comstock/Cornell; and Scott Weidensaul's > "Living on the Wind: Acoss the hemisphere with migratory birds" > published by North Point Press. Both discuss Peter Berthold's findings > that pretty much proved that migratory distance and direction in many > obligate migratory birds are strongly controlled by genes via > Mendelian breeding studies of the Blackcap (a > *Sylvia* warbler from Eurasia). When Berthold bred birds with short distance > and long distance migration patterns he was able to produce medium distance > migrant birds (as measured by period of migratory restlessness in > captivity). Similar studies documented a genetic component of migratory > direction. This being said, it is also known that many waterfowl and the > cranes learn migration routes from social relationships, often in families, > but also from mates in succeeding years. A lot of a bird's ability to > navigate and determine how to far to migrate appears to be inborn, which can > be deduced, as Maurice aptly noted, from the evidence of young birds > migrating without much benefit of companionship from experienced birds on > their first trips to the wintering grounds. Many young seabirds and > shorebirds depart the nesting grounds long after their parents have deserted > them. Is migration a simple one-gene phenomenon? Certainly not - it's a > complex array of behaviors controlled by lots of genes and experiences. > Return trips by young birds and subsequent migrations as adults have a huge > learned component in addition to the inborn navigational aids for making the > trip. > > For the most part feeders do not much affect the behavior of > long-distance migratory birds such as warblers, hummingbirds, > tanagers, or orioles. Although occasional Rose-breasted Grosbeaks and > Baltimore Orioles overwinter at feeders in eastern North America the > vast majority of their kind continue to journey to the tropics for the > winter months. Nonetheless, if increased survival of large numbers of > birds could be aided by feeders it's plausible that a population that > *already* has a genetic tendency to winter somewhere could be > increased by bird feeding (e.g. the foregoing discussions on hummers). > A similar situation has also been shown for the Blackcap by Berthold > and his students in the case of a recently established and increasing > wintering population that migrates from the mainland North Sea coast > to southern Britain where new plantings and warming climate have made > it possible for them to survive the northern winter. Several birds > appear to employ both a short distance and long distance migration > strategy - Gray Catbirds regularly winter all along the eastern > seaboard in small, but not insignificant numbers, while most others go > to the tropics. > > Feeders also can affect migrants such as finches and raptors that rely > on lack of food to influence their urge to move on. For instance, > declines in migration counts of Sharp-shinned Hawks have coincided > with huge increases of sharp-shins on CBCs in the Northeast. What > could hold Sharpies up North? How about flocks of juncos and House > Finches at northern feeding stations? > > Good Birding, > > Walter Ellison > > 23460 Clarissa Road > Chestertown, MD 21620 > phone: 410-778-9568 > e-mail: rossgull@crosslink.net > > "A person who is looking for something doesn't travel very fast" - E. > B. White (in "Stuart Little") > > ----- Original Message ----- > From: "Maurice Barnhill" > To: > Sent: Wednesday, December 10, 2003 10:02 AM > Subject: Re: [MDOSPREY] Human intervention > > >> Gerald & Laura Tarbell wrote: >> >>> All points taken with interest. However, wasn't some of the research >>> that Lorenz and others did with geese evidence that migration is >>> learned behavior, possibly not genetic, as you claim? If it is >>> learned, then it might even be possible to teach them to fly north >>> for the winter. Of > course, >>> they might starve as a result, but the point I am making is that >>> your genetic origin seems to be more assumed than proven. Any other >>> thoughts > out >>> there on this? >>> Jerry >>> >>> >> Geese migrate in family groups, so it is possible that some or even >> all migration behavior is learned. However, in many and probably >> most species the young migrate separately from the adults, so it is >> hard to see how their behavior could be learned. >> >> I agree that my comments do not apply to geese and that there may be >> other species whose migratory behavior is learned. >> >> -- >> Maurice Barnhill > > ====================================================================== > = > To leave the MDOsprey list, send e-mail to listserv@home.ease.lsoft.com > with the following message in line 1: signoff mdosprey > ======================================================================= > ======================================================================= To leave the MDOsprey list, send e-mail to listserv@home.ease.lsoft.com with the following message in line 1: signoff mdosprey ======================================================================= =========================================================================